PROJECT 2 ? PROJECT SUMMARY The overall objectives are to understand and define the cellular mechanisms that contribute to the development and progression of biliary tract cancer, termed cholangiocarcinoma (CCA). Advances in CCA therapy will require an understanding of molecular signaling pathways, and validation of targeted agents coupled with biomarkers for patient selection. Both the Hippo and fibroblast growth factor receptor 2 (FGFR2) signaling pathways have been implicated as oncogenic mediators in CCA. In this application, we unify these observations by positing cross-talk between the Hippo and FGFR2 signaling pathways in CCA. Consistent with this concept, we have generated preliminary data demonstrating that Hippo signaling via activation of the transcriptional co-activator YES-associated protein (YAP) drives expression of FGFR2, and in turn FGFR2 signaling mediates YAP activation. Further evaluation of the pathway demonstrates tyrosine phosphorylation of YAP that appears to be dependent on Src family kinases (SFKs). Tyrosine-phosphorylated YAP in turn associates with TBX5, driving oncogenic transcriptional activity. From a pre-clinical therapeutic perspective, inhibition of FGFR2 signaling induces tumor cell death in patient derived xenografts with YAP nuclear immunoreactivity but not in those negative for this marker of Hippo pathway signaling. Based on these preliminary data, we propose the central hypothesis that CCA progression can be driven by FGFR2-mediated YAP tyrosine phosphorylation by SFKs. We will now employ current and complementary molecular, biochemical, and cell biological approaches, and preclinical CCA models to examine this hypothesis. Our specific aims will test three hypotheses. First, that YAP drives specific FGFR2 expression, which in turn promotes YAP signaling by: (a) FGFR-mediated SFK activation and YAP tyrosine phosphorylation; and (b) Tyrosine-phosphorylated YAP co-activated by the TBX5-mediated transcriptional expression of FGFR family members. Second, by that YAP nuclear localization serves as a biomarker for response to FGFR2- targeted therapy: (a) In unselected patient-derived xenografts (PDX) treated with an FGFR inhibitor; and (b) In conjunction with evidence for a YAP activation signature in PDX. Finally, that inhibition of FGFR signaling is therapeutic in patients with CCA: (a) In FGFR2 fusion negative / YAP nuclear positive CCA patients receiving INCB054828, a panFGFR inhibitor, in the setting of a clinical trial; and (b) By interruption of Hippo signaling pathways. The proposal, which is technically and conceptually innovative, is also highly significant because it identifies new mechanisms for CCA oncogenic signaling and will help identify therapeutic strategies for the treatment of CCA, namely FGFR inhibition coupled with a biomarker (i.e., nuclear YAP localization) for patient selection.